Radiofrequency amplifying system



Jan. 7, 1930.V s, COHEN 1,742,694

RADIOFREQUENCY AMPLIFYING SYSTEM Filed 0G12. 15. 1925 2 Sheets-Sheet l MAMA.

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Patented Jan. 7, 1930 UNITED STATES PATENT y OFFICE SAMUEL COHEN, OF BROOKLYN,. NEW YQRK BADIOFREQUNCY AMPLIE'YIN'G` SYSTEM Applicationl filed` October 13, 1925. SerialpNo. 762,298.`

of frequencies without interference inthev 1o several circuits of the amplication system from undesired oscillatory current.

Another object of my invention is to provide a circuit arrangement in an electron tube amplification system in which high resistances are introduced in the electron tube circuits at selected intervals for damping oscillat-ions arising from self-osclllation of the several. tubes while not interfering with the normal amplification of the signaling energy.

Still anotherobject'of my invention is to provide means in the circuits of the amplifying system for absorbing undesired oscilla.-v

tory currents and rendering such current ineffective to interfere with signaling currents without damping the signaling energy. Y

A further obj ect of my invention is to provide a bridge arrangement of resistors for connection with relation to the input and output circuits of each of the electrontubes of a radiorfrequency amplification system for damping self-oscillatory currents independent of the amplification of the signaling energy over a wide band of frequencies.

My invention will be more fully understood from the following specification by reference to the Laccompanying drawings, wherein i Figure 1 is a diagrammatic view illustrating one embodiment vof my invention in an electron tube emplification system; Fig. 2

- shows a modified arrangement of the resistors in the several stages of a radio frequency amplifier system; Fig. 3 illustrates an arrangement of resistorsin one of the stages of an electron tube amplification system in the forni of a balanced bridge; Fig. 4 is a theoretical diagram of the circuit arrangement shown in Fig. 3; and Fig. 5 shows an appli- 5o cation of the balanced circuit of Fig. 3 to a two stage radio frequency amplifying system of a radio receiver.

Referring to the drawings in more detail,

reference characters 1, 2 and 3 designate elec,

'tron tubes each having grid,V filament and Vplate electrodes. Theelectron tubes 1 and 2 v are arranged to function as amplifiers of high frequency radio energyl while the electron tube 3 operates as a detector of the radio frequency signaling energy. "The receiving apparatus is shown in connection with anxantenna system 4 having a primary winding 5 connected therewith with a connection 'to ground 6. A secondary winding? is induc-V tively coupled with the primary-winding 5 andthe secondary circuit tunedto. the frequency of the signal desired to be received by mean-s oit-variable tuning condenserY 3. The

output circuit of electron tube 1 includes the primary winding `9 of the radio frequency coupling ltransformer 10,', secondary winding 11k of which is tunedby means of variable condenser 12. The output circuit of the second stage of radio frequency amplification formed by electron tube 2 is connected with a primary winding 14 of the radio frequency coupling transformer 15 having a'secondary winding 16 tuned by means of variable condenser 17. The tube 3 includes a grid condenser 18, and grid leak 19 in the grid circuit thereof. The amplificationsystem operates over a wide band of frequencies where the transformers lOand 15 are electromagnetically` coupled and the lperiodicity ofthe circuits adjusted by meansl of variable condensers 8, 12 and 17, and by properly appor- 'the rectifier tube 3 at different potential than is supplied to the plate circuits of tubes 1 and 2. A suitable responsive device 23 is connected in the output circuit of the rectifier tube 3.

It is well known that unstable conditions exist at particular frequencies when the electron tube circuits are timed. Each of the stages of amplification is subject to self-excitation as a result of which regenerative currents are set up between the input and output circuits of each of the tubes resulting in the production of undesired circulating currents and the generation'ofundesired oscillations.

In order to prevent the instability of the amplification system and the undesired oscillation thereof, I provide means in the electron tube circuits which while not effective `whenithe system is not in oscillation, become effective to prevent oscillation of the ampliication system when undesired circulating currents become existent in the amplifier circuits. I insert non-inductive resistors R1 in veach of the grid leads of the radio frequency amplifying circ-uit as illustrated in Fig. 1. I may insert these resistors as represented at R3 and R4 in Fig. 2 of the drawings, in

. the filament leads of the several tubes in the amplification system.) These resistors each act as an absorbing medium when the system becomes unstable and oscillates, but when the system is not in condition of oscillation the resistors are not effective.V The reason for this will be readily appreciated when it is observed that the introduction of several hunchai'acteristics of the circuit with respect to the passage of signaling energy.V However, when a condition of oscillation exists, then the oscilating current must traverse the resistance R1 and R2, orfR3 and R.l and be absorbed thereby.

I provide additional means for preventing oscillatory currents in the tube. circuits by introducing a non-inductive resistance R5 in the plate circuit of the detector tube 3 so that oscillatory currents which may be passed through the detector tube 3 are absorbed and prevented from entering the audio frequency circuits of the receiving system. The interposition of resistance R5 in the output circuit of thev detector tube 3 has been found very effective in the elimination of stray oscillations which may pass through the audio frerquency amplifying system: by the capacity couplings offered by the electrodes of the tube The value of eachof the resistors'Rl, R2,-

RS. R4 and Rr is not critical, butinust be ini- ,tiallyy set -when the circuits are adjusted in the vreceiving apparatus. I provide condensers24, 25 and 26A which serve as by-pass condensers for radio frequency currents.

In Fig. 3 I have shown another method of Y accomplishing the desirable results of the elimination of the unstable condition in each stage of a radio frequency amplifier. In this arrangement a bridge method is provided with the resistors 'disposed in the bridge arms for obtaining a complete balance. In Fig. 3 I have shown an electron tube 2 having its input circuit connected with secondary winding 10 timed by variable condenser 12. |The tube 2 contains a filament or cathode 2a, a grid or control member 2b, and a plate or anode 2. The inherent intra-electrode capacity existent bet-Ween the grid electrode 21? and plate electrode 2c is represented by condenser Gc. The output or plate circuit of the tube 2includes the primary winding 14 of transformer 15 to which secondary 16 is coupled. The resistors R1 and R2 form two arms of a bridge circuit represented in Fig.

4 where condenser C., is the compensating capacity arranged to balance the grid capacity Grc which is connected in circuit with the resistor R2. I have found that in methods heretofore employed for neutralizing capacbridge arrangement of. my invention over- Y comes difficulties experienced in the past for Ythere 1s no apparent change in the bridge arms of the inductancesy or variation of distributed capacity for variation of frequency. In the theoretical diagram shown in Fig. 4

i I have lindicated by klike numerals of ref-y dred ohms of series resistance in the filament lgrid circuit which is normally many thousand ohms in resistance will not alter the dampingl erence the parts which appear in the circuit diagramv of Fig. 3. The non-inductive resistors R1 and Rgare shown positioned in the arms of a bridge opposite to the capacities of G.. and Cc.

' In Fig. 5 `I have shown an application of the bridging circuit of Figs. 3 and 4 to a radio .25, and 26 are the radio frequency by-pass condensers as described in connection with Figs. 1 and 2. The non-inductive resistance R5 positioned in the plate circuit of the tube 3 operates to absorb undesired oscillatory currents which may pass through the radiofrequency amplifier stages and the detector tube 3. In Fig. 5 the tube 1 is illustrated as having the 'balancing resistors Rl and R2 in circuit therewith, while the tube 2 has resistors R( and R7 in circuit therewith.

My invention has proven very practical in its construction and operation, and while I have described certain embodimentsof the invention, I desire that it be understood that modifications may be made and that no limi? tations upon the invention are intended other than those imposed-by thescope of the appended claim. v

What I Cla-inland desire to secure by Letters Patent of the United States is as follows: In a radio frequency amplifying system the combination of a plurality of electron tubes, each having grid, cathode and plate 5 electrodes, an input circuit including the grid and cathode electrodes of each of said tubes, an output circuit including the plate and cathode electrodes of each of said tubes, with the output circuit of one of said tubes inter- 10 linked with the input circuit of a succeeding tube, and a high non-inductive resistance device having one point thereof connected with said cathode electrode and the opposite ends thereof connect-ed one directly with said grid 15 electrode and the other end thereof capacitively connected to said grid electrode through an auxiliary condenser, the plate electrode and the inherent capacity between said grid and plate electrodes for balancing o the capacity coupling of said tubes.

In testimony whereof I aix my signature.

SAMUEL GOHEN. 

